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Forced Ferment Test

We’ve all had that moment of panic and doubt. You brewed a beer that’s stuck up higher than you’d like. Was the beer just not as fermentable as you’d thought? Maybe you mashed warm, maybe your extract is poorly fermentable or maybe the yeast is in poor health. One important data point to obtain is the brew’s absolute terminal gravity. In professional breweries this information is known for their brews and the way to find it is the classic Forced Ferment Test.

To perform the test, you need a sanitized growler or flask and a pint of wort, just after pitching the yeast is best. Ideally you should have a magnetic stir plate (that you use for your yeast starters, right?). Place the pitched wort sample into the growler covered with foil and stir on high for 2 or 3 days. Measure the gravity. This is your absolute minimum terminal gravity. If you don’t have a stir plate, you should swirl the sample as often as possible.

A ferment that is ideal for producing flavorful beer will probably never hit this absolute gravity, but it should come within a few points. If your beer isn’t at the end of primary you might want to consider re-pitching the brew with fresh yeast.

If you have a stuck brew, try removing a small sample and performing a forced ferment test on it with fresh yeast and nutrient. This will let you know if you should re-pitch the beer to bring it down further or if the beer is high by nature.

The Phantom doesn’t do this test on every batch of beer brewed, but if the beer is made with an unusual technique, ingredients or a high starting gravity the results are great to have. tpb

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